The present invention relates to an altitude sensing control apparatus, and more particularly, to such apparatus which receives pneumatic inputs and develops a pneumatic output.
Many applications require altitude sensing control apparatus. For example, for aircraft gas turbine engine applications, it is often necessary to provide switching intelligence as a function of altitude. In one such application, altitude sensing control apparatus is utilized to operate an air valve which controls a flow of air toward an engine part. A typical use of such altitude sensing control apparatus is described in copending application of Wallace M. Schulze, Ser. No. 71,502, filed Aug. 31, 1979, now U.S. Pat. No. 4,304,093, issued 12/8/81, entitled "Variable Clearance Control for a Gas Turbine Engine," and assigned to the assignee of the present application. This copending application is hereby incorporated by reference to the present application.
As pointed out in the above-mentioned application of Ser. No. 71,502, altitude sensing control apparatus may be employed to pneumatically develop a pneumatic output signal to operate an air valve which controls a flow of air to the aircraft engine for controlling the clearance between rotating blades and a blade shroud in the engine. Such pneumatic operation eliminates the need to convert from operating mediums, such as engine fuel or oil, to a pneumatic output for operating the air valve. For such aircraft engine applications, it is essential that the output of the altitude sensing control apparatus be accurate, repeatable, and reliable. As such altitude sensing control apparatus may employ a portion of the compressor discharge to operate the air valve, the control apparatus is likely to be subject to relatively high temperatures, e.g., up to 1000.degree. F.
Accordingly, it is a general object of this invention to provide improved altitude sensing control apparatus.
Another object of the present invention is to provide such apparatus which develops an accurate, repeatable, and reliable pneumatic output signal for operating an air valve.
Another object of the present invention is to provide such apparatus which develops a pneumatic output signal of relatively smaller pressure level for altitudes below a predetermined altitude and which develops a pneumatic output signal of relatively greater pressure level for altitudes greater than the predetermined altitude where the smaller pressure level does not operate the air valve while the greater pressure does operate the air valve.
Another object of the present invention is to provide such apparatus with operability indication means.
Another object of the present invention is to provide such apparatus which includes failure backup means for ensuring a desirable pneumatic output signal under failure conditions.